CCR5 and plague: In vitro studies showed, however, that although the Ccr5-deficient macrophages have a drastically reduced uptake of Yersinia pestis (an isolate from a fatal human case of plague), they experience a similar mortality with the wild-type Ccr5-expressing macrophages (55), suggesting that, if this model is representative to humans, the CCR5 deficiency did not have a protective effect against plague in people (56).